Operation of drilling processes offshore, control of pipelines offshore or onshore requires real-time information about conditions, being downhole, along a pipeline or between two installations along a pipe line. Information regarding a pipelines' own status, regarding a remote status, regarding a downhole status or commands from a remote location to a downhole location, from an onshore location to an offshore location all needs communication paths for transfer of data. New and more sophisticated drilling techniques require an increased bandwidth for communicating telemetry signals in real-time from downhole to surface stations. The industry standard for these kinds of transmission is mud pulse telemetry that uses the drill pipe to guide acoustic waves in the drilling fluid; this technique will typically render bit rates in the sub 10 bit/sec. Such slow rates is incapable of transmitting a large amount of data in real-time. Acoustic telemetry through drill pipes have been studied with bit rates in sub 100 bit/sec.
A number of conventional systems have a wire in the drill pipes; however these systems suffer from poor reliability and high cost due to a large number of electrical connectors.
Current coupled inductive couplers in drill pipes are known and have been tested out. Such transformer cable connecting systems have also been tested for transmission of data along pipelines both onshore and offshore.
However none of the methods indicated above provides a system that in a reliable fashion can transfer data at a high bit rate along a pipeline either being onshore or offshore.
From the patent literature there are known methods that overcome some of the drawbacks indicated above. GB 2 184 581 A discloses a shut off valve control system for an oil or gas platform, where the valve is operated by command signals from a control station transmitted on a guided micro-wave carrier via a pipe.
It is further known from WO 02/071643 A1 a communication device for transmitting signals between a substation control unit and a control unit of bay elements comprising transceiver devices connected to the substation and the bay element control units and a wave guide enclosing and connecting antennas of said transceiver devices. The transceiver devices produce electromagnetic radio frequency airwaves to communicate information between the control units. The disclosed solution is not particularly well suited for offshore use as water is not a good medium for transmitting high frequency electromagnetic waves.
Another example of communication arrangement along a pipeline is disclosed in U.S. Pat. No. 6,515,592 B1 (Babour et al.). This invention is directed to power and signal transmission using insulated conduit. In one embodiment it is shown a sandwich solution in which an electrical current path is defined by a casing encapsulated by an insulator with a conductive layer for return of electrical current in a layer surrounding said insulator. The conductor-insulator-conductor configuration maintains the traditional signal loop of a feed and return path.
Yet another example of a communication system is disclosed in US 2005/0024231 A1 (Fincher et. al). This document proposes a system in which a conductive pipe receives a solid insulator layer on the interior running along the pipe and a suitable reflective shield forming an inner surface of the insulator layer. This sandwich configuration employs RF signals in the insulator layer.
Hence, according to one aspect of the invention it is provided an arrangement which in a secure fashion transmits data for automation, control or monitoring along a pipeline at a much higher bit rate than known from prior art indicated above.